Gaseous discharge device



Mayv19; 1959 J. M. LAFFVERTY lGAsEoUs DISCHARGE DEVICE Filed 001'.. 17,1957 Inventor- James M Laffer-zf,

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the number of units in" seriesA 2,887,614 GAsoUs DISCHARGE nnvrcn JamesM.Laierty, Schenectady, NX., assignor to General Electric Company, 'acorporation of New York application october 17, 1951, serai No. 690,851)1o Claims. (c1. 315-36) Therpresent inventionl relates to gaseouselectric discharge devices of the voltage-regulator type. Moreparticularly, the invention relates to improved voltage-regulator tubesuniquely adapted for high voltage operation. Voltage-regulator tubes-aretwo-element cold-cathode gas discharge devices which `are ionized tobecome conductive at a voltage denominated as breakdown voltage, and4sustain a' glow discharge having a constant potential differencebetween the electrodes thereof over a substantial range of current.Although, ideally, this potential difference or regulating voltage isconstant, in commercially availablevoltage-regulator tubes theregulating voltagevaries` greatly with current.

1 Since the` regulating voltage in a voltage regulator tube is dependentprimarily upon the gas and the cathode material utilized, in designing agaseous` voltage-regulator tube to regulate at a particular voltage, onemay readily select the gas-cathode material combination whichcharacteristically regulatesjfat the desired voltage. The highest suchregulating voltage which can be maintained stable in a gaseous voltageregulator devicek is approximately 400 volts. This voltage is obtainedutilizing carbon dioxide gas and a copper cathode. Hydrogen gas with acopper cathode gives a Astable regulating voltage of 325.volts.

It is impossible to maintain a stable gas glow discharge at highervoltages a single voltage regulator tube. In order that higher voltagesbe regulated, it is necessary to operate anumber of voltageregulatortubes in series. This` has aV number' of disadvantages, among whichV are`that it 4is highly `wasteful of space and that the tubes, beingsubjected to different temperatures, operate under diferent conditions.V

Accordingly, it is an object of theipresentinvention to provide avoltage regulatorgaseous discharge device capable ofy providingavoltage. reference at higher voltage than has heretofore beenobtainable.

A further object of the invention isto provide a flexible voltageAregulator" device unit which can be combined with other` similar umtsto,` form a single device capable of regulating any desiredhighvoltage'.`

A further object of the invention isto provide compact voltage regulatorgaseous discharge devices which occupy an extremely small space and`which'may be operated at extremely high temperatures.

In accord with the present inventionl 'provide a noble gasffilledVvoltage regulator unit comprising an anode vand a cathode' having planeparallel symmetry insulating'ly' joined together'with a ceramic memberproviding a thin disk-like tube, the thickness of which is small withrespect to theldimeter thereof. A suitable breakdown gap is provided tocause breakdown to occur at a The'voltage regulator unit may be or maybeformed in combination with so that any desired reguus'ed separately,

lating voltage maybe obtained,

The novelflifeatures"believedcharacteristic of the invention are setforth inthe appendedclaims. The invention itself, to'xgf'e't'her furtherobjects and advan- 2,887,614 Patented May 19, 1959 f'ice Fig 4illustrates one-alternative device of Fig. l,

Fig. 5 is a cut-away perspective view of a plurality of the devices yofFig. 1 assembled in series, and

Fig. 6 is a voltage-current characteristic of a` multiunit device asillustrated in Fig. 5, constructed in accordwith the present invention.In Fig. l voltage regulator unit 1 comprises `a cathode disk 2 and ananode disk3 in plane parallel spaced relation and hermeticallyjoined byan annular insulating member 4 having a counterbore 5 at onelongitudinal end thereof and an annular groove 6 in the surface ofcounterbore 5; Counterbore 5 and groove 6 form a shielded space 7 whichis not in direct line with the main volume 8 of unit 1. A rod-like anodepin 9 is located at the geometrical center of the unit andiselectrically and mechanically connected to the interior surface of anodedisk 3 and forms with cathode disk 2, a breakdown gap 10. The entireinterior volume of unit l is filled with a highly purified stable noblegas which may consist of helium, neon, argon, krypton, xenon or mixturesthereof. The exact gas or mixture of gases selected to ll the interiorof the tube depends upon the desired regulating voltage, since thepotential difference between cathode and anode during normal glow dis'-charge of the tube is primarily a function of the gas and the cathodematerial utilized. i v

Although cathode disk 2 and anode disk 3 may be of any highly conductivemetal,v such as copper, they are preferably fabricated ,from titanium.Titanium is used to obtain optimum characteristics from the devicesbecause of the unique Vgettering characteristics thereof. I havediscovered that one of the conditions necessary for .the achievement ofa substantially uniform potential dif- .substantial range of operating4currents thereof, is the maintenance of high gas purity.v If -auy smallquantity of a chemically reactive gas other than the noble gas intendedto be utilized is present -Within the tube, the characteristics changemarkedly with use. Accordingly, the voltage regulator tubes of thepresent invention are filled with an atmosphere consisting of a stablenoble gas o r a mixture of stable noble gases While the device is beingsealed in accord with the invention disclosed and claimed in mycopending application Serial No. 690,849 filed October 17, 1957,herewith and assigned to the present assignee.

in accord with my copending application gaseous dischar-ge devices whichutilize a noble gas iilling are formed 'by `the sealing of titaniummembers and a titaniummatching ceramic member or members while the tubeis maintained in an atmosphere of the operating gas at a suitablepressure. When titanium is heated to the temperatures (of the order of700 C. to 1100 C.) at which titanium may be bonded to titanium-matchingceramics, the metal is an excellent getter for chemically active gaseousimpurities commonly present' in noble gases such as CO2, H2, H2O, N2 andO2 and the like. When the devicesof the present invention areso formedthe resultant atmosphere comprises highly purified noble embodiment tothe 3 gases ora mixture of noble gases. As a result of this, the voltageat which the device maintains a stable glow discharge remains constantfor several orders of magnitude, `a condition heretofore unobtainable inprior art voltage regulator tubes.

Annular insulating member 4 comprises a refractory ceramic insulating`material, the coeicient of thermal expansion of which is a close matchfor lthat of titanium, and which hence may be suitably bonded at hightemperatures to form hermetic seals with titanium cathode disk 2 andanode disk 3. Such a ceramic is a sintered agglomerate of silicon oxide,magnesium oxide and aluminum oxide denominated as Forsterite. One suchForsterite ceramic and the method of preparation thereof is disclosedand claimed in the copending application of,A.`G. Pincus, Serial No.546,215, tiled November 10, 1955,r and assigned to the assignee of thepresent invention.

YThe shape of annular insulating member 4 is of great importance in thedevices constructed in accord with the present invention. Sincev thedevice is extremely thin it is necessary that complete insulation bemaintained throughout the life of the device between cathode 2 and anode3. For this reason, insulating member 4 is, of course, electricallynon-conductive. However, during the life of the tube metal is sputteredfrom the cathode onto the inner side wall of insulating member 4 forminga metallic surface. Such a metallic surface can constitute a leakagepath which effectively short-circuits the tube. This is avoided,however, by counterbore 5 and annular groove 6 in insulator 4 whichstructure effectively forms a surface region which is not in directcontact or within the line of sight of the cathode. Accordingly, themetal which is sputtered on the walls does not cover this surfaceportion and insulation between cathode 2 and anode 3 is maintainedthroughout the life of the device.

Anode pin 9 may be constructed of iron, titanium., tungsten, molybdenum,stainless steel or any other material conventionally used for electrodesin electron or gaseous discharge devices which does not readily alloywith the titanium anode 3 at the sealing temperature.

Electrode 9 terminates short of cathode 2 and defines therewith abreakdown gap 10. In a voltage regulator tube it is desirable that thebreakdown voltage be as close to the regulating voltage as is possible.From Paschens law it is known that the potential at which gaseousbreakdown occurs between two electrodes in a particular atmosphere, forthat particular atmosphere and for the particular cathode materialutilized, is a function only of the product of the gas pressure timesthe gap length. One may plot the well-known Paschen curves, a group ofwhich are illustrated in Fig. 2 of the drawing. In Fig. 2, the breakdownpotential for Varying gap lengths for argon gas at a pressure of 10, 20and 40 mm. of mercury are represented by curves A, B and C respectively.From these curves it may be seen that there is a particular gaplength-gas pressure product at which the breakdown voltage is a minimum.Accordingly, breakdown lgap 10 in device 1 is chosen to be substantiallythat distance which, in combination with the gas pressure and cathodematerial utilized, causes breakdown to occur at the minimum of thePaschen curve for the gas, gas pressure, and cathode material utilized.

In accord with another feature of the present invention, anode pin 9 maybe omitted. In this embodiment it is necessary that another 'breakdowngap be established. This may be done as follows: anode pin 9 is omittedin construction. Once formed the tube is subjected to a supply voltageof approximately 100 volts in excess of its designed regulating voltage.Breakdown then occurs, and a glow discharge fills space 8. The currentis then pulsed intermittently at a value of approximately 1 ampere persquare centimeter for several hours. This high-current glow dischargecauses a large amount of metal to be sputtered from the cathode anddeposited upon the inner surface of annular insulating member 4. Theannular gap between counterbore 5 of member 4 and anode disk 3 thenconstitutes the breakdown gap for the device. In this embodiment thisgap is adjusted to the criteria set forth with respect to gap 10, sothat the gap distance-gas pressure product is substantially equal to theminimum of the Paschen curve for the lgas and cathode material utilized.

In devices constructed in accord with the present invention a distinctadvantage is attained by the unique geometry wherein cathode and anodea-re extremely close together. This geometry is not conventional and isnot derived merely by placing anode and cathode as close together as ispossible. In order to understand the criteria governing thejuxtaposition of anode and cathode in devices in accord with the presentinvention, reference is made to Fig. 3 of the drawing. In Fig. 3, thecharacteristic normal glow discharge, which characteristic is universalfor inert gases, is represented schematically. The most importantportions of the glow in Fig. 3 are the cathode dark space, the negativeglow, the Faraday dark space, and the positive column, all of which areidentified with captions in Fig. 3. The curve of Fig. 3 is a graphicalrepresentation of the potential distribution between anode and cathodein the tube illustrated, and corresponds thereto. As may readily beseen, the greatest portion of the potential difference between thecathode and the anode is found in the region of the glow denominated thecathode dark space with only a gradually varying and small potentialdifference between the beginning of the negative glow and the anode.

Accordingly, I have found that it is possible to construct voltageregulator tubes in accord with the present invention by pushing theanode up through the positive column and into the Faraday dark spacenear the negative glow region so that actually only a portion of theconventional glow discharge is utilized. The portion utilized, however,contains the greatest portion of the potential difference normally foundin more extended discharges. Accordingly, the distance between thecathode and the anode in the device of Fig. 1 is substantially thedistance between the cathode and the beginning of the Faraday dark spacein Fig. 3 of the drawing. While this distance varies for differentgases, different pressures, and cathode materials utilized, thedistances for the inert gases and the cathode materials utilized in thepresent invention may be readily determined by those skilled in the artso that it is relatively easy to determine the precise distances whichsatisfy the condition that the cathode and anode be separated by adistance substantially equal to the width of the cathode dark space andthe negative glow for the gas, electrodes, and pressure utilized. Thus,for any given gas and electrode material combination, the distance fromthe cathode to the Faraday dark space times the gas pressure is aconstant. VAccordingly, the distance to the Faraday dark space can becomputed for any gas at any pressure once this constant is known. Fortitanium electrodes, these constants are: 0.64 for argon, 0.80 forxenon, 0.90 for neon and 1.72 for helium, where the pressure isexpressed in mm. of Hg and the distance is expressed in cm.

In accord with a further feature of my invention, greater exibility maybe attained in the matter of adapting the voltage regulator tubes fordifferent voltages. This is attained by coating the interior surface ofcathode disk 2 with a low work function material to attain a lowregulating voltage. Thus, for example, rto attain a regulating voltageof 75 volts, for a single unit, an atmosphere of argon may be combinedrwith a surface of barium. This may be achieved by coating cathode disk2 with a layer approximately 0.001" thick or less of barium aluminideprior to assembling the tube. Other materials such `a lmating, and' inwhichthe anode .,prirthasbeen eliminatedis illustratedinperspectiveinFi'g. f4,` `In the device of Fig;` 4, coating 11 is the cathodesurfaceand annular gap 12 is the. breakdown fgap.

A decided advantage `of the present invention is that iu addition tothe-fact that the regulating gasI and cathode material may be chosen toprovide a given regulating voltage-within a range cit-fromvapproximately ,75 to 180 volts, a plurality of devices as illustratedlinqFig. l` may be combined when a voltage higher than that which may beregulated with a ynoble ,-gas vis desired Vto be regulated. In Fig. ofthe drawing there is-illustrated a device comprising a 'plurality of theunits as lillustratedr in Fig. 1 eachlof which comprisesa-separate noblegas filled compartment "combined to regulate a high voltage. Devieessuch as illustrated in Fig," 5f comprise a plurality of the devicesastillustrated in ylig. 1 stacked in series. Since there is no necessityfor having both anodeand eathode disks' for the intermediate tube'units, a single disk 13 forms anode and cathode for adjacent tube unitsand is substantially thinner than cathode end wall member 14 and anodeend wall member 15. These devices may be made in accord with theinvention described and claimed in my aforementioned copendingapplication, thus achieving the advantages of high noble -gas purityand, consequently, a stable regulating voltage over a wide range ofcurrents. Tubes such as those illustrated in Fig. 5 of the drawing havebeen constructed with ceramic annular members as small as 0.068 thick.Since, in these tubes the thickness of the anode and cathode plates`when the tubes are stacked together is approximately 0.015", oneachieves a design parameter of approximately 2 volts per 0.001 or 2kilovolts per inch of the tube length utilized.

In tubes constructed in accord with the present invention, the diameterof the tube determines its current carrying capacity. The tubes of thepresent invention are capable of carrying extremely high currents,considering the size utilized. Utilizing xenon gas and titanium cathodesfor example it has been found that the ratio j/ p2 where j is thecurrent density and p is the pressure of gas utilized, which ratio is aiigure of merit for voltage regulator tubes, has been found to be14x10-e amperes per square centimeter per millimeter of mercury squared.As a practical matter, in tubes constructed in accord with the presentinvention, approximately twice this current density has been drawnwithout appreciably increasing the regulating voltage exhibited by thetube.

In Fig. 6 of the drawing, there is shown the voltagecurrentcharacteristic (curve A) for a three cell tube similar to the oneillustrated in Fig. 5 having a diameter of 1 with an effective cathodediameter of 0.7". This tube was charged with approximately 20 mm. ofxenon and the electrodes were of titanium. This characteristic may becompared with curve B which is a similar characteristic for 3 standardOD3V-R tubes and one OA3V-R tube connected in series which regulate inthe same voltage range. As may be seen from the drawing, the tubeconstructed in accord with the present invention exhibits an extremelyilat characteristic denominating a nearly constant regulating voltageover a substantial range of current. Since the devices of this inventioncontain only metal and ceramic they may be operated at extremely hightemperatures.

While the invention has .been described hereinbefore `with respect tospecific embodiments thereof, it will beV v posed `between andforminglhermetic seals with said cathode and said vanode members, saidinsulating membe'r having a re-entran't 'cross-'sectien which 'providesa surface portion thereof .which Yis shielded Afrom -the volume definedby" said cathode and said anode members; a highlyfpuriiied noble.gastmo'sphereliillir'ig Ithe interior of s'aid device; and meanselectrically'connecte'd between said `ane-ae' and js'aia cathodedefining 'a closely spaced4 br'eakdewn gap between.

`2. he device of claim lv wherein said an'ode and cathode members are oftitanium. l

` 3. A noble Igas voltage regulator gaseous electric disi charge devicecomprising: a disk-shaped cathode member and a disk-shaped anode memberin plane parallel spaced relation, the distance between said cathode andsaid anode being substantially equal to the distance from the cathode ofthe Faraday dark space on the normal glow discharge characteristic forthe gas, gas pressure, and electrode material utilized; an annularinsulating member interposed between and forming hermetic seals withsaid cathode and said anode members, said insulating member having acounterbore in one surface thereof and an annular groove in saidcounterbore; a highly puried inert gas filling the interior of saiddevice; and means electrically connected between said cathode and saidanode defining a closely spaced breakdown gap therebetween.

4. 'Ihe device of claim 3 wherein said anode and cathode members are oftitanium.

5. A high voltage noble gas voltage regulator gaseous electric dischargedevice comprising in parallel spaced relation, a disk-shaped metalliccathode end wall member, a disk-shapedmetallic anode end wall member,and at least one disk-shaped metallic member interposed between saidcathode and said anode, the distance between adjacent metallic membersbeing substantially equal to the distance from the cathode to theFaraday dark space on the normal glow discharge characteristic for thegas, gas pressure, and electrode material utilized; a plurality ofannular insulating ceramic members separating said metallic members fromone another, hermetically sealed to said separated members, and forminga plurality of separate sealed compa-rtments, each of said insulatingmembers having a reentrant cross-section providing a surface portionthereof which is shielded from the volume defined by said metallicmembers juxtaposed thereto; a highly purified noble gas atmospherefilling each of said compartments; and means connected between each ofsaid juxtaposed pair of metallic members providing a closely spacedbreakdown gap therebetween.

6. The device of claim 5 wherein said metallic members areof titanium.

7. A high voltage noble gas voltage regulator gaseous electric dischargedevice comprising in plane parallel spaced relation, a disk-shapedmetallic cathode end wall member, a disk-shaped metallic anode end wallmember, at least one disk-shaped metallic member interposed between saidcathode and said anode; a plurality of annular insulating ceramicmembers separating said metallic members from one another, hermeticallysealed to said separated members, and forming a plurality ofseparatesea-led compartments, said insulating members each comprising anannulus having a counterbore in one end thereof and an annular groove inthe surface of said counterbore; a highly purified noble gas atmosphereiilling each of said compartments; and means electrically connectedbetween each pair of juxtaposed metallic memasszeu bers providing aclosely spacedbre'akdown gap therebetween.

8. The device of claim 7. wherein said metallic members are oftitanium.y

9. A high voltage noble gas voltage regulator gaseous electric dischargedevice comprising in plane parallel spaced relation, a ldisk-shapedmetallic cathode end wall member, a disk-shaped metallic anode end wallmember, and at least' one disk-shaped metallic member interposed betweensaid cathode and said anode,v the distance between adjacent metallicmembers being substantially equal to the distance from the cathode tothe Faraday dark space on the normal glow discharge characteristic forthe gas,` -gas pressure, and electrode material utilized; a plurality ofannular insulating ceramic members separating said metallic members fromone another, hermetically sealed to said separated members, and forminga plurality of separate sealed compartments,

said insulating members each comprising an annulush'aving a counterbo'reat one end thereof' andan'annular groove inthe surface of saidcounterbore;,a highly purified noble gas atmosphere illing each ofsaidcompartments; and means electrically connected between adjacent metallicmembers providing a closely'spaced breakdown'gap therebetween.

10. The device of claim 9 wherein said metallic mem# bers are oftitanium.

References Cited in the le of this patent UNITED STATES PATENTS FranceNov. 2o, '1944

